Lindsay turned herself over to authorities today and began serving out her 35-day house arrest sentence ... but what does that actually mean for Lohan?

L.A. Sheriff's spokesman Steve Whitmore said today in a statement:

"She is now confined to the interior premises of her home at all times."

Translation: No clubbing, shopping, dining out for at least two weeks.

Whitmore also explained Lohan was granted house arrest due to good behavior but also because of overcrowding at the jails and budgetary constraints. And her ankle bracelet will not be detecting drugs or alcohol. Whew!

If Lohan behaves herself and stays at home, her sentence could be reduced from 35 days to just 14. If police are alerted to any movement outside the luxurious Venice Beach pad, via her tracking device, the sentence could be extended or she may even be required to do real jail time.

Whitmore declined to say whether any exceptions would allow Lohan to leave her home, but she might be granted leave for nearby work-related appointments. The actress is gearing up to star as the wife of John Gotti, Jr. in a biopic of the infamous New York mob family, but shooting is set to start later this year so it isn't expected to interfere with Lindsay's time at home.

Lohan will still be required to perform 480 hours of community service, but the judge forbade the actress from doing so while under house arrest.